When characterising electromagnetic fields, the problem of disruptive field contributions generally occurs. This problem occurs because superposition of a wave emitted directly from an antenna with wave portions which are scattered by the ground sometimes leads to significant measurement errors. The relatively large distance (measurement distance) between a measuring probe and the test antenna to be measured results in a shallow angle of incidence of the directly generated wave on the ground. This problem occurs in particular with so-called antenna far field measuring systems. As a result, the directional graph of the test antenna cannot be measured directly because of the field portions which are scattered on the ground.
In order to improve the measuring method, it is therefore desirable to suppress the portions of the measurement signal scattered on the ground. This is achieved, for example, by the measuring probe and the test antenna being arranged so as to be elevated relative to the ground in order to achieve the longest possible time delay before the signal emitted is detected by the receiver. The suppression of the field portions scattered on the ground is carried out, for example, by means of high-speed switches.
Alternatively, so-called vertical probing of the measuring probe is known in order to determine the undulation produced by the superposition of the direct and scattered signal portion and to take this into consideration globally as a correction variable in the measured antenna graphs.
Another method for suppressing field portions which are scattered on the ground involves placing scatter bodies which are as irregular and absorbent as possible along the ground in order to prevent signal portions which are reflected in a specular manner on the ground.
However, none of the methods known from the prior art is capable of completely preventing the superposition of the direct signal portion with the signal portions scattered by the ground and so any measurement is still prone to errors. In particular in the case of shallow angles of incidence on the ground, it is barely possible to suppress the scattered field portions effectively or to eliminate them from the measurement result.